Electroless nickel plating



United States Patent 3,152,009 ELECTROLESS NICKEL PLATING Herbert K. De Long, Midland, Mich, assignor to The Dow Chemical Company, Midland, Mich, a corporation of Delaware No Drawing. Continuation of application Ser. No. 725,510, Apr. 1, 1958. This application May 17, 1962, Ser. No. 195,405

7 Claims. (Cl. 117-130) This invention relates to the deposition of nickel by chemical reduction as opposed to electrolytic deposition and is more particularly concerned with a bath therefor and a method for the electroless deposition of nickel on magnesium, aluminum, iron and brass and other catalytic basis metals.

This application is a continuation of my prior-filed application Serial No. 725,510, filed April 1, 1958, now abandoned, which was a continuation-in-part of application Serial No. 663,871 filed June 6, 1957, now abandoned.

In United States Patent 2,532,283, Brenner, there is described a method of nickel plating by chemical reduction. This patented process uses nickel chloride or nickel sulfate in combination with a hypophosphite to accomplish deposition of nickel on a metallic surface without the application of an electric current. This process has variously been called electroless or chemical nickel plating. However, when magnesium is placed in the Brenner bath, substantial etching of the magnesium and foaming occurs as the acid solution attacks the metal, or else, the magnesium dissolves in the solution and replaces the nickel therein. Thus, the Brenner bath has not been suitable for the deposition of nickel on magnesium.

Another United States Patent 2,694,019, Gutzeit, shows the feasibility of using fluoride concentrations below 0.12 mole per liter, but indicates that greater concentrations of fluoride ion decrease the plating rate and adversely affects the stability of the bath. This patent, however, shows only the use of nickel chloride as the source of nickel ions. When magnesium is placed in the Gutzeit bath, a similar result is obtained as is obtained vwith the Brenner bath, i.e., etching and foaming of the magnesium surface.

Where the use of magnesium metal is desired because of its structural advantages including strength and reduced weight, but because its wearability or resistance to corrosion does not meet the requirements of a particular application, coating with a nickel surface would be desirable. This nickel coating would increase the corrosion resistance and Wearability of the magnesium base material without appreciably aflecting its structural and Weight advantages. Representative applications where the process can be utilized to increase wear resistance and resistance to corrosion of various base metals include printing plates, aircraft tubing, fluid couplings, internal combustion engine parts, electronic equipment parts having complex shapes, etc. ticularly those shapes dificulty plateable by conventional electrolyte methods. Another use of the nickel surface is as a base for subsequent coatings of copper, chromium, tin, nickel, zinc, cadmium, silver, gold, etc., using conventional baths and procedures.

It is, therefore, a principal object of the present invention to provide an electroless nickel plating bath suitable for use on magnesium. Another objectof the present invention is to provide an electroless nickel plating procedure applicable to magnesium and which results in a nickel plate which is continuous, hard, semi-bright, has good adhesion, and which can be bufled to a mirror-like surface. A further object of the present invention is the Other applications are also possible, par-' provision of an electroless nickel plating procedure whereby hydrogen fluoride, nickel salts other than nickel chloride or sulfate, a compatible hypophosphite ion, an organic acid salt and optionally potassium or ammonium fluoride are mixed in an aqueous solution, and used to treat a catalytic basis metal surface, such as, iron, aluminum, brass or magnesium metal surfaces, at a pH between 3.5 and 7.0 and at a temperature between and 212 degrees Fahrenheit thereby to yield a hard, adherent, semi-bright, nickel plate on the metal. Other objects will become apparent hereinafter.

The foregoing and additional objects have been accomplished by the provision of an electroless nickel plating bath comprising nickel ions, fluoride ions, and hypophosphite ions in water. This bath also must contain at a maximum only trace quantities of chloride ion and sulfate ion. It has been found that such a bath will plate magnesium without attack of the magnesium. In order to maintain the nickel in solution, a pH for the bath below 7.0 is required and to prevent excessive attack of the metal to be plated, a pH below about 3.5 is usually avoided. Preferably, the pH is maintained between 5.0 and 6.8 and the most desirable pH is 6.5 for most uses. Control of the pH may be accomplished by adding ammonium hydroxide, hydrogen fluoride, or other acidic or basic materials compatible with the bath. Preferably, a watersoluble organic acid salt is employed as buffering agent to maintain pH control. Representative salts of organic acids which may be employed as buffers include, for example, sodium citrate, sodium succinate, sodium tartrate, sodium phthalate, sodium lactate, potassium citrate, etc. that is, a soluble salt which affects the pH so as to maintain the solution in the desired pH range. The presence of the fluoride ion is usually accomplished by the addition of a 50 percent aqueous solution of hydrogen fluoride, however, fluoride salts may be employed, such as, for example, sodium, potassium, ammonium, nickel, etc. fluorides. By the addition of fluoride salts where hydrogen fluoride is also employed, some mass action repression of the hydrogen fluoride is obtained, thereby affording some pH control. When hydrofluoric acid is used as a 50 percent aqueous solution, quantities from 5.7 cc. per liter to 98 cc. per liter may be employed to obtain a final bath concentration between .15 and 2.5 moles per liter of fluoride. Preferably the mole per liter concentration of fluoride employed is from .15 to .75 and desirably at .32 mole per liter.

The concentration of the nickel ion in the final bath may be varied from .04 to 1.4 moles per liter, but is preferably present in concentrations from .08 to .32, from .04 to .16 mole per liter also being satisfactory and desirably a concentration of .08 mole per liter is used. Unexpectedly, it has been found that nickel chloride and nickel sulfate may not be used in the bath and process of the present invention as the source of nickel ions. When these materials are employed, extensive gassing of magnesium occurs. Therefore, the use of nickel chloride or nickel sulfate is not contemplated within the scope of this invention and are specifically excluded herefrom. While basic nickelous carbonate is usually employed to obtain the nickel ion concentration, other soluble nickel salts which will furnish the nickel ion to the final bath, such as, for example, nickel carbonate, nickel cyanide, nickel fluoride, nickel acid fluoride, nickel hydroxide, nickel oxalate, nickel oxide, nickel phosphide, nickel hypophosphate, etc. may be used. A water-soluble salt of a hypophosphite is employed such that the resulting gram ion concentration of hypophosphite ion is between .04 and 2.6 moles per liter, preferably .04 to .55 mole per liter and desirably .18 mole per liter. To achieve a concentration of hypophosphite ion of .18 mole per liter, 20 grams per liter of NaH PO -H O are employed.

When a bath of the above composition has been prepared, it may be used to treat a catalytic metal surface which has been cleaned to remove any oxide, oil, or other surface contamination which might be present. If such surface contaminations are allowed to remain, a firmly adhered nickel plate is not usually obtained. Either brushing with a steel brush, sand blasting, or the use of pickling and surface activating pre-treatments may be employed. The surface activation and cleaning techniques are conventional and are used in a conventional manner to provide a relatively clean surface for the deposition of the nickel. The article to be plated after surface treatment is immersed in a bath such as hereinbefore described while a bath is maintained at a temperature from 90 to 212 degrees Fahrenheit, preferably from 160 to 212 degrees Fahrenheit, and desirably at 170 to 180 degrees Fahrenheit. The surfaces to be plated are immersed in the bath at the pre-seleeted temperature for a period of time from 3 minutes to a number of hours depending upon the particular characteristics of the plate desired. Thereafter, the article is separated from the bath, washed to remove any bath residue, and, if desired, buffed to give a hard, bright, adherent, nickel plate having thicknesses up to and above three thousandths of an inch.

While the bath of the present invention is particularly suited for magnesium, it may be used on other catalytic basis metal, such as, for example, iron, aluminum, brass, etc. surfaces with facility. The bath of the present invention appears to be more stable than the prior art baths by virtue of the absence of substantial precipitation as is found in prior art baths after use.

The following examples are given to illustrate the process and bath of the present invention but are not to be construed as limiting the bath or process thereto.

Comparative Prior Art A Mg base alloy having a nominal composition of 3 percent aluminum, 1 percent zinc, balance magnesium, panel Whose dimensions were 1 inch by 2 inches by 0.040 inch were immersed in a conventional nickel chloride electroless nickel solution of the following composition: (US. Patent 2,532,283Brenner).

NiCl 6H O grams/liter 30 NaH PO 'H O dO. NH Cl do 50 Na C H O SH O, sodium citrate do 100 pH 8.4 Temperature degrees Fahrenheit- 170-1 80 A similar panel to that used above was immersed in an acid fluoride electroless nickel bath of the following composition:

HF (50 percent) milliliters/1iter 7 2NiCO 3Ni(OH) -4H O grams/liter NaH PO -H O dO... N9-3C5H507'5Hz0' dQ. KF do 10 pH 6.5 Temperature degrees Fahrenheit 175 The original weight of the panel was 10.6718 grams and the weight of the panel after 30 minutes immersion was 10.8551 grams or a weight gain of .1833 gram. The plating rate for thickness was 0.0006 inch per hour of a continuous, hard, semi-bright metallic in color, nickel plate having a good adhesion to the magnesium surface. There was no evidence of chemical attack on the basis metal.

Example 2 To show that increased plating rates may be obtained from increased fluoride concentrations, the following baths were prepared and the procedure of Example 1 repeated with the folowing results:

HF (70%) cc./l 5 2NiCo +3Ni(OI-I) -4H O gm./l 10 NaH PO -H O grn./l 20 N33C5H507' gm./l Temperature F pH 6.5 Rate, 0.0001" per hour.

HF (70%) cc./l 5 2NiCO +3Ni(OH) -4H O gm./l 10 NaH PO -H O gm./l Na C5H5O72H2O gm./l NH HF gm./l 5 Temperature F 175 pH 6.5 Rate, 0.0005" per hour.

HF (70%) cc./l 5 2NiCO -3Ni(OH) -4H O gm./l 10 NaH PO -H O gm./l 20 Na C H O '2H O glTL/l NH HF gm./1 10 Temperature F 175 pH 6.5 Rate, 0.0008" per hour.

HF (70%) cc./l 5 2NiCO -3Ni(OH) -4H O gm./l 10 NaH PO -H O gm./l 20 Na C I-I O -2H O gm./l NH HF gm./l 15 Temperature F 17 5 pH 6.5 Rate, 0.001 per hour.

HF (70%) cc./1 5 2NiCO -3Ni(OH) -4H O gm./l 10 NaH PO 'H O gm./l Na C H O '2H O gm./l NH HF gm./l 20 Temperature F 175 pH 6.5 Rate, .0010" per hour.

HF (70%) cc./l 5 2NiCO -3Ni(OH) -4H O gm./l 10 NEHZPOZ'HZO gm./l Na C H5O72H2O gm./l NH HF gm./l 25 Temperature F 175 pH 6.5

Rate, .0012" per hour.

with all of the above baths, a bright, nickel deposit having good adhesion was obtained.

Example 3 Other examples of baths which have been used to give bright and adherent electroless nickel deposits are:

NiF -4H O gm./l 14 NaH PO -H O gm./l 20 Na C H O 5H O gm./l KF gm /1 1O Temper ature F 175 pH 6.8 Rate, 0.0009" per hour.

HF (50%) cc./l 7 2NiCO -3Ni(OH) -4H O gm./l 10 NaH PO -H O gm./l 20 Na3C5H5O75H gm./l KF gm./l 10 Temperature F 175 pH 6.5 Rate, 0.0009" per hour.

HF (50%) cc./l 7 Nico g /1 10 NaH PO -H O g./l Na3C H507'5H2O g./l. KF g./l 10 Temperature F 175 pH 6.5 Rate, 0.0010" per hour.

HF (50%) /l 7 2NiCO -3Ni(OH) -4H O g./1 10 NaH2PO2'H2O g./1 N33C5H5072H20 g./l KF g./l 10 Temperature F-.. 17 5 p 6.5 Rate, 0.0008" per hour.

HF (70%) cc./l 5 2NiCO -3Ni(OH) -4H O g./l 10 NEHZPOZ'HZO g./1 N21 C H O -2H O g./l 10 NHJ-IF g /l 10 Temperature F 175 pH 6.5 Rate, 0.0008" per hour.

HF (70%) cc./l 5 2NiCO '3Ni(OH) -4H O g./l 10 NaH PO -H O g./l 20 Na3C5H507'2H2O g./l KF g./l 20 Temperature F 175 p 6.5 Rate, 0.0010 per hour.

HF (70%) cc./l 5 2NiCO -3Ni(OH) -4H O g./l l0 NaHzpogHzo g./1.. N33C5H5072Hz0 g./l NH4HF2 g./l 20 Temperature F 175 P 6.5 Rate, 0.0010" per hour.

6 Example 4 Many types of magnesium alloys have been plated utilining the baths of the present invention including:

While the invention has been particularly described with respect to magnesium and the magnesium base alloys, it is to be understood that the bath and process of the present invention are applicable to other catalytic basis metals including, for example, iron, aluminum, aluminum base alloys, brass, etc.

The term magnesium used herein and in the appended claims means magnesium and the magnesium base alloys in which the magnesium content exceeds 75 percent by weight.

Various modifications may be made in the bath and method of the present invention without departing from the spirit or scope thereof and it is to be understood that I limit myself only as defined in the appended claims.

I claim:

1. A process for electroless nickel plating which comprises;

immersing a magnesium based metal article in an aqueous solution maintained at a temperature of from about to about 212 F., said aqueous solution consisting essentially of from about 0.15 to about 2.5 moles fluoride ion per liter of said aqueous solution, from about 0.04 to about 1.4 moles nickel ion per liter of said aqueous solution and from about 0.04 to about 2.6 moles hypophosphite ion per liter of said aqueous solution, said solution containing at a maximum only trace quantities of chloride and sulfate ions and being buffered to a pH between about 3.7 and 7.0.

2. A process for electroless nickel plating which comprises;

(1) immersing a magnesium based metal article in an aqueous solution maintained at a temperature of from about 90 to about 212 F., said aqueous solution consisting essentially of from about 0.15 to about 2.5 moles fluoride ion per liter of said aqueous solution, from about 0.04 to about 1.4 moles nickel ion per liter of said aqueous solution and from about 0.04 to about 2.6 moles hypophosphite ion per liter of said aqueous solution, said solution containing at a maximum only trace quantities of chloride and sulfate ions and being buttered to a pH between about 3.7 and 7.0,

(2) maintaining the article in said solution for at least 3 minutes, and

(3) separating the nickel plated article from said solution.

3. A process for electroless nickel plating which comprises;

(1) immersing a magnesium based metal article in an aqueous solution maintained at a temperature of from about 90 to about 212 F., said aqueous solution consisting essentially of from about 0.15 to about 2.5 moles fluoride ion per liter of said aqueous solution, from about 0.04 to about 1.4 moles nickel ion per liter of said aqueous solution and from about 0.04 to about 2.6 moles hypophosphite ion per liter of said aqueous solution, said solution containing at a maximum only trace, quantities of chloride and sulfate ions. and being buffered to a pH between about 3.7 and. 7.0,

(2) maintaining the article in said solution for at least 3 minutes, and

(3) separating the nickel plated article from said solution, and

(4) washing the nickel plated article to, remove bath residue therefrom,

4. A process for electroless nickel plating, which comprises;

(1) immersing a magnesium based metal article in an aqueous, solution maintained at a temperature of from about 90 to about, 212 F., said aqueous solution consisting essentially of from about 0.15 to about 0.75 mole fluoride ion per liter .of said aqueous solution, from about 0.08 to about 0.32 mole nickel ion per liter of said aqueous solution and from about 0.04 to about 0.55 mole hypophosphite ion per liter of said aqueous solution, said nickel ion being obtained from a nickel compound selected from the group consisting of basic nickelous carbonate, nickel carbonate, nickel cyanide, nickel fluoride, nickel acid fluoride, nickel hydroxide, nickel oxalate, nickel oxide, nickel phosphide and nickel hypophosp-hate, said solution containing at a maximum only trace quantities of chloride and sulfate ions and being bufiered to a pH between about 5.0 and 6.8,

(2) maintaining the article in said solution for a period of time of from about 3 minutes to a number of hours, and

(3) separating the resulting nickel plated articles from said solution.

5. A process for electroless nickel plating which comprises;

(l) immersing a magnesium based metal article in an aqueous solution maintained at a temperature of from about to about 212'F., said aqueous solution consisting essentially of about 0.32 mole fluoride ion per liter of said aqueous solution, about 0.08 mole nickel ion per liter of said aqueous solution, said nickel ion being furnished substantially from nickel carbonate and about 0.18 mole hypophosphite ion per liter of said aqueous solution, said solution containing at a maximum only trace quantities of chloride and sulfate ions and being buifered'to a pH of about 6.5,

(2) maintaining the article in said solution for a period of time of from about 3 minutes to a number of hours, and V (3) separating the resulting said solution.

6. A bath for nickel plating by chemical reduction of magnesium and its alloys consisting essentially of an aqueous solution of a nickel salt and a hypophosphite and a fluoride, wherein't-he nickel ion is furnished essentially from nickel carbonate and wherein the concentration of nickel is .04 to 1.4 moles .per liter, of hypophosphite ion is .04 to 2.6 moles per liter, and of fluoride ion is .15 to 2.5 moles per liter, buifered to a pH between 3.5 to 7.0.

7. A bath for nickel plating by chemical reduction of magnesium and its-alloys consisting essentially of an aqueous solution of a nickel salt and a hypophosphite and a fluoride, wherein the nickel ion is furnished essentially from basic nickel carbonate corresponding to the empirical formula 2NiCO -3Ni(OH) -4H' O and wherein the concentration of nickel is .04 .to 1.4 moles per liter, of hypophosphite ion is .04 to 2.6 moles per liter, and of fluoride ion is .15 to 2.5 moles per liter, buflfered to a pH between 3.5 to 7.0.

nickel plated article from Gutzeit l Nov. 9, 1954 Puls Dec. 8, 1959 

1. A PROCESS FOR ELECTROLESS NICKEL PLATING WHICH COMPRISES; IMMERSING A MAGNESIUM BASED METAL ARTICLE IN AN AQUEOUS SOLUTION MAINTAINED AT A TEMPERATURE OF FROM ABOUT 90 TO ABOUT 212*F., SAID AQUEOUS SOLUTION CONSISTING ESSENTIALLY OF FROM ABOUT 0.15 TO ABOUT 2.5 MOLES FLUORIDE ION PER LITER OF SAID AQUEOUS SOLUTION, FROM ABOUT 0.04 TO ABOUT 1.4 MOLES NICKEL ION PER LITER OF SAID AQUEOUS SOLUTION AND FROM ABOUT 0.04 TO ABOUT 2.6 MOLES HYPOPHOSPHITE ION PER LITER OF SAID AQUEOUS SOLUTION, SAID SOLUTION CONTAINING AT A MAXIMUM ONLY TRACE QUANTITIES OF CHLORIDE AND SULFATE IONS AND BEING BUFFERED TO A PH BETWEEN ABOUT 3.7 AND 7.0. 